摘要
超宽带(UWB,Ultra-Wideband)脉冲无线电是一种可以和其它通信系统共享频谱资源的新型无载波通信技术。为了实现频谱共享,UWB系统通常采用极低功率谱密度的超短脉冲作为信息的载体;为了实现信息的有效解调,UWB系统通常采用多次重传的方式来提高接收信噪比。考虑到多址接入及FCC(Federal CommunicationsCommission,联邦通信委员会)频谱掩模的限制,UWB系统为每一用户分配一个唯一的伪随机序列,利用这些伪随机序列来调制用户的数据信息,实现多用户通信并平滑发射信号的频谱。UWB系统具有隐蔽性好、抗多径和窄带干扰能力强、传输速率高、系统容量大、功耗低、可以和其它通信系统共享频谱等一系列优点。然而利用UWB技术也面临着一些严峻的挑战,其中定时同步及信号解调是制约UWB技术发展的两项关键技术。
定时同步是实现信号能量捕获的前提,可以说没有定时同步,信号解调就无从谈起。由于UWB系统中承载信息的是占空比极低的超短脉冲,且该系统常工作在稠密多径环境中,所以实现精确的定时同步是一项艰巨的任务。传统的RAKE接收技术需要估计信道信息且对定时误差异常敏感(纳秒量级的定时抖动就会引起接收机性能的急剧下降),在UWB通信系统中应用RAKE技术面临着复杂度高、抗定时抖动性差的尴尬局面。针对这些问题,本论文对UWB系统的同步及对应的解调算法进行了较深入的理论研究,提出了两种低复杂度的UWB同步算法和三种能有效对抗定时抖动的、不需要信道估计的UWB同步解调联合算法:
1、基于DS(Direct Sequence,直接序列)码匹配滤波的无数据辅助UWB同步算法:将观测信号和其一个帧周期的延迟信号相乘,利用帧长度的积分清零器(I&D,Integrate-and-Dump)对相乘后的信号进行积分、采样。将离散采样值通过DS码匹配滤波器即可建立用于搜索同步参数的目标函数。DS码的伪随机性,使得目标函数类似冲激函数,且同步时刻对应目标函数最大值的出现时刻。由于UWB通信网络中各用户的DS码是相互独立的(具有近似正交性),多用户干扰(MUI,Multiple User Interference)通过DS码匹配滤波器后不会产生明显的峰值,所以本同步算法可以直接应用到多用户通信环境中。
2、非搜索UWB同步算法:现有的UWB同步算法大都是先使用某种方法构建目标函数,然后搜索该目标函数的最大(小)值,用最大(小)值的下标刻画同步参数。由于目标函数值的获得通常需要大量繁琐的计算,所以避免搜索过程是降低UWB同步算法复杂度的有效途径。基于这一考虑,本文提出了一种基于巴克码的非搜索UWB同步算法。在算法实现中,首先在发送端发送周期延拓的4位巴克码序列,在接收端对观测信号进行延迟、相关、采样等操作得到一系列离散样本值,然后利用这些样本值和最小二乘准则计算出符号头部能量与符号尾部能量,最后利用这两个能量值得到同步参数的闭式解。
3、SR-UWB系统的同步及解调算法:RAKE解调技术需要先通过信道估计建立解调模板,然后将解调模板和接收信号作相关得到判决变量,最后利用判决变量检测出发送信息。由于UWB信道通常是密集多径的,所以精确估计UWB信道具有极大的计算复杂度。另外,UWB信号的持续时间短、占空比低的特点使得RAKE接收机对定时误差异常敏感,纳秒量级的定时抖动就会引起接收机性能的急剧下降。为避开复杂的信道估计过程及增加UWB接收机的抗定时抖动性,本文提出了两种适用于SR-UWB(Single Reference UWB,单参考UWB)系统的、不需要信道估计的、能有效对抗定时抖动的同步解调联合算法。算法一先通过重叠相加、能量检测等方法建立目标函数,然后搜索目标函数的最大值,用最大值的下标表示同步参数,并顺带构造出解调模板,最后利用这一解调模板和同步参数估计值及TH(Time-Hopping,跳时)码的先验信息构造判决变量,将判变量通过符号检测器实现信息解调。算法二则更加充分地利用了SR-UWB系统独特的信号结构和TH码的先验信息。在实际实现中,首先利用I&D器件得到一系列离散样本值,通过对这些样本值的平方、平均操作建立目标函数,搜索目标函数的最大值位置即可获得同步参数,再利用同步参数选择I&D器件的输出样本值,将所选的样本值通过符号检测器即可实现信息解调。由于算法二不需要另外构造解调模板,且在同步阶段就利用了TH码的先验信息,所以算法二的性能要优于算法一。
4、DTR-UWB系统的同步解调联合算法:为了在接收端避免信道估计过程,研究者们提出了TR-UWB(Transmitted Reference UWB,传输参考UWB)系统。该系统通过发送不承载信息的参考脉冲,利用参考脉冲的冲激响应作为信息脉冲的解调模板的方式,避免了信道估计过程。显然,参考脉冲的发送势必会降低通信速率和能量利用率。针对这一缺陷,人们又提出了DTR-UWB(Differential TransmittedReference UWB,差分传输参考UWB)系统。本文针对DTR-UWB系统设计了一种同步解调联合算法。通过对观测信号的加权平均及延迟相关操作得到一系列离散帧率(采样间隔为一个帧周期)的采样值,利用这些样本值可同时实现同步捕获和信息解调。加权平均操作提高了接收信噪比,从而提升了同步解调性能;帧率采样及采样值的重复利用有效地降低了系统复杂度。
5、基于巴克码的同步解调联合算法:利用4位巴克码特有的自相关特性,本文提出了冗余模板(RDT)解调算法和非冗余模板(NRDT)同步解调联合算法。这两种算法都是直接从观测信号中提取解调模板,然后和接收信号作相关,利用符号检测器实现信息解调。虽然RDT算法不需要同步过程,具用极低的复杂度,但是RDT中存在不含有用信息的噪声段,该段的存在影响了接收机的性能。为了剔除冗余噪声段,本文又在RDT算法的基础上提出了NRDT算法。该算法首先利用能量检测的方法获得同步参数,然后利用同步参数剔除RDT中的噪声段。由于NRDT算法剔除了冗余段,所以和RDT方案相比,NRDT方案有更低的误码率。由于这两种方案的解调模板是从接收信号中提取的,在定时误差出现的情况下,仍然能捕获到大部分的信号能量,因而它们都有很强的抗定时抖动性。
理论分析及计算机仿真都证明本文所提同步及解调算法比同类算法具有更优的性能。
Ultra-wideband impulse radio (UWB-IR) is a promising technology for data communications in short-range indoor applications. It is characterized by the transmission of ultra-short pulses (in the sub-nanosecond scale) at low power spectral density. In order to keep the signal spectrum within the Federal Communications Commission (FCC) mask and obtain adequate signal energy for reliable detection, a single information symbol is represented by several pulses, each located in its own frame. To accommodate multiple-access and smooth transmit spectrum, pseudo random timing-hoping (TH) spread codes or/and direct-sequence (DS) spread codes are often employed. Interest in UWB is motivated by several features including: ample multipath diversity, low-complexity baseband transceivers, a potentially large user capacity, and potential to overlay existing narrowband systems. To harness these benefits, however, UWB-IR faces several challenges, among which synchronization and demodulation are particularly critical at the receiver end.
Synchronization is a performance-critical factor in most communication systems, especially in UWB transmission. It stems from the fact that the transmitted pulses are very narrow and have low power. The dense multipath channel, through which the pulses bearing information propagate, is unknown at the receiver during the synchronization phase. Moreover, the bit error rate (BER) of UWB is very sensitivity to mistiming, the timing errors as small as fractions of a nanosecond can seriously degrade the system performance. To cope with these challenges, a number of synchronization and demodulation algorithms have been proposed in this dissertation. Summarized as follows:
Relying on the prior knowledge of the DS codes, a non-data aided synchronization algorithm is proposed for DS-UWB systems. It remains operational in practical UWB settings with unknown multipath propagation. With the aid of the integrate-and-dump (I&D) over a frame duration and peak-picking from the output of the DS codes matching filter, the proposed approach can achieve frame-level timing acquisition within one symbol duration. The maximum significantly differs from other values due to the pseudo random property of the DS codes. Therefore, the proposed scheme has high immunity to noise effects.
A data-aided synchronization scheme dispensing with searching procedure is proposed in this dissertation. With the help of judicious training symbols and symbol-level samples, the energy values of the truncated tail and head of the received symbol waveform can be obtained. With the two energy values in hand, frame-level timing acquisition can be acquired in closed form. It is worth noting that with the perfect knowledge of the multi-path channel, the proposed scheme can achieve timing synchronization at any desirable resolution. The proposed algorithm only exploits symbol-level samples and without searching process, thus it turns out to not only speed up synchronization, but also enjoys low-complexity.
Regarding demodulation, RAKE is the first receiver considered for UWB systems. Unfortunately, this classical approach will cause high re- ceiver complexity since a large number of fingers are required to estimate. Furthermor, RAKE is very sensitivity to mistiming, the timing errors as small as fractions of a nanosecond can significantly degrade the system performance. To bypass channel estimation and enhance the robustness to mistiming, the single reference UWB (SR-UWB) system is proposed. Relying on the unique signal structure of SR-UWB, two joint synchronization and demodulation algorithms are proposed without employing any training sequences (non-data aided). With the aid of overlap-add method and energy detection technique, the first approach can acquired timing acquisition even if in the presence of inter-frame interference (IFI) and inter-symbol interference (ISI). With the synchronization parameter being available, the demodulation template can be easily constructed. Taking advantage of the synchronization parameter and the demodulation template, the decision statistic, which is then passed through a sign detector to result in the symbol estimates, can be attained by using of the correlation operation. In the second algorithm, in terms of the unique signal structure and the prior knowledge of the TH codes, the objective function can be established over a short observation interval. Peak-picking the objective function, the synchronization parameter can be acquired. After timing acquisition, the samples used to achieve synchronization can be re-utilized for the demodulation process by a zero-crossing comparator. As a result, the implementation complexity is markedly reduced in comparison with the first approach.
Based on the prior knowledge of the DS codes, a joint blind synchronization and demodulation scheme is developed for differential transmitted reference UWB (DTR-UWB) systems. The proposed approach can achieve frame-level synchronization with the help of frame-rate samples. Taking advantage of the periodicity of the DS spread codes, the frame-level synchronization can be carried out even in one symbol interval. On the other hand, after timing acquisition, these frame-rate samples can be re-utilized also for the demodulation by a zero-crossing comparator. Thus the acquisition time and the implementation complexity are reduced considerably. Meanwhile, the noise cross noise effect is alleviated because a wide-sense average operation has been executed in synchronization phase, which is responsible for the enhancement of the detection performance. It is also worth noting that the proposed approach can be employed in multi-user scenarios without any modification.
By the special auto-correlation pattern of the proposed training sequence (4 bits Baker codes), a redundance-included demodulation template (RDT) is constructed from the received signal. When the RDT is available, two approaches can be selected to detect transmitted information symbols. One is to demodulate transmitted symbols directly by the RDT, which does not require timing acquisition, and thereby has considerably lower complexity. The alternative is to first carry out timing acquisition by invoking simple energy detection, which is employed to shear the RDT to obtain a non-redundance-included demodulation template (NRDT), and then demodulate transmitted symbols by the NRDT. Although the second approach has higher complexity (depending on the level of timing error desired), it can obtain better BER performance compared with the first one owing to canceling the redundant noise. Furthermore, the demodulation template is derived from the received signal, so both approaches can avoid the effect of pulse distortions and cope with the timing error.
Simulations and theoretical analyses validate that the proposed approaches which have been stated above enjoy better performances in comparison with the similar ones in terms of acquisition probability, normalized mean square error (NMSE) and BER.
引文
[1]张中兆,沙学军等(译).超宽带无线电技术:Ultra-wideband radio technology.北京:电子工业出版社2005.9
[2]王金龙,王呈贵,阚春荣等.无线超宽带(UWB)通信原理与应用.北京:人民邮电出版社,2005.
[3]葛利嘉,曾凡鑫,刘郁林等.超宽带无线通信.北京:国防工业出版社,2005.
[4]Porcino D.,Hirt W.,"Ultra-wideband radio technology:potential and challenges ahead," IEEE Commun.Mag.,vol.41,no.7,pp.66-4,Jul.2003.
[5]Rappaport T.S.,Annamalai A.and Buehrer R.M.,etc."Wireless communications:past events and a future perspective," IEEE Commun.Mag.,vol.40,no.5,pp.148-161,May 2002.
[6]Yang L.and Giannakis G.B.,"Ultra-wideband communications:an idea whose time has come," IEEE Signal Process.Mag.,vol.21,no.6,pp.26-54,Nov.2004.
[7]Assessment of Ultra-Wideband(UWB) Technology,OSD/DARPA,Ultra -Wideband Radar Review Panel.R-6280,Jul.1990.
[8]FCC First Report and Order:In the matter of revision of Part 15 of the Commission's Rule Regarding Ultra-Wideband Transmission Systems,FCC 02-48,Apr.2002.
[9]任品毅,廖学文,梁中华(译).超宽带通信原理及应用:Ultra-Wideband Communications Fundamentals and Applications.西安:西安交通大学出版社2007.
[10]Thomas E.,"Walk don't run:the first step in authorizing ultra-wideband technology,"IEEE Conference on Ultra-Wideband Systems and Technologies (UWBST),vol.23,May 2002.
[11]屈静,超宽带通信系统中基于能量捕获的同步研究[学位论文],北京:北京邮电大学,2008.
[12]Fontana R,Ameti A and Richley E,etc."Recent advances in ultra wideband communications systems," In Proc.IEEE UWBST,pp.129-133,May.2002.
[13]Carbonelli C.and Mengali U.,"Synchronization algorithms for UWB signals,"IEEE Trans.Commun.,vol,54,no.2,pp.329-338,Feb.2006.
[14]Yang L.,Tian Z.and Giannakis G.B.,"Non-data aided timing acquisition of ultra -wideband transmissions using cyclostationarity," in Proc.Int.Conf.Acoust., Speech, Signal Process., pp. 121-124, Apr. 2003.
[15] Tian Z. and Giannakis G. B., "Data-aided ML timing acquisition in ultra-wideband radios," in Proc. Conf. Ultra-Wideband Syst. Technol, pp.142-146. Nov., 2003.
[16] Carbonelli C., Franz S. and Mengali, U. etc, "Semi-blind ML synchronization for UWB transmitted reference systems," Thirty-Eighth Asilomar Conference on Signals, Systems and Computers, vol. 2, pp. 1491-1495, Nov. 2004.
[17] Carbonelli C. and Mengali U., "Timing recovery for UWB signals," IEEE Global Telecommunications Conference, vol. 1, pp. 61-65, Dec. 2004.
[18] Irahhauten Z., Nikookar H., Janssen, G. J. M, "An overview of ultra wide band indoor channel measurements and modeling," IEEE Microw. Wireless Compon.Lett., vol. 14, no. 8, pp. 386-388, Aug. 2004.
[19] Wang Fei and Lv Tiejun, "An improved kalman filter algorithm for UWB channel estimation," ChinaCOM' 2008. pp. 50 - 54. Aug. 2008.
[20] Carbonelli C., Mitra U., "Clustered ML Channel Estimation for Ultra-Wideband Signals," IEEE Trans. Wireless Commun., vol. 6, no. 7, pp. 2412-2416, Jul.2007.
[21] Tian Z. and Giannakis G. B., "BER sensitivity to mistiming in ultra-wideband impulse radios-part I: fading channels," IEEE Trans. Signal Process., vol. 53, no.5, pp. 1897-1907, May 2005.
[22] Tian Z. and Giannakis G. B., "BER sensitivity to mistiming in ultra-wideband impulse radios-part II: nonrandom channels," IEEE Trans. Signal Process., vol.53, no. 4, pp. 1550-1560, Apr. 2005.
[23] Ying Y., Ghogho M., Swami A., "A new non-coherent demodulation scheme for IR-UWB," IEEE 8th Workshop on Signal Processing Advances in Wireless Communications, pp.1 - 5, Jun. 2007.
[24] Ying Y., Ghogho M. and Swami Ananthram, "Block-coded modulation and noncoherent detection for impulse radio UWB," IEEE Signal Process. Lett., vol.15,pp. 112-115,. vol.15, 2008.
[25] Raphaeli, D., "Noncoherent coded modulation," IEEE Trans. Commun., vol. 44,no.2,pp. 172-183,1996.
[26] Gong Ping, Lv Tiejun and Qu Jing, "A novel quasi-4PPM modulation for UWB systems with corresponding synchronization scheme," The 4th International Conference on Wireless Communications, Networking and Mobile Computing, pp. 1-4, Oct. 2008.
[27] Luo X. and Giannakis G. B., "Low-complexity blind synchronization and demodulation for (ultra-) wideband multi-user ad hoc access," IEEE Trans. Wireless Commun., vol. 5, no. 2, pp. 1930-1941, July 2006.
[28] Win M. Z. and Scholtz R. A., "Impulse radio: how it works," IEEE Commun.Lett. vol. 2, no. 2, pp. 36-39, Feb. 1998.
[29] Win M. Z. and Scholtz R. A., "Ultra-wide bandwidth Time-hopping spread-spectrum impulse radio for wireless multipath-access communications,"IEEE Trans. Commun., vol.48, no. 4, pp. 679-691, Apr.2000.
[30] Chen X. and Kiaei S., "Monocycle shapes for Ultra Wideband system," in Proc.Intl. Conf. on Circuits and System, pp. 597-600, May. 2002.
[31] Wu L., Lottici V. and Tian Z., "Maximum likelihood Multiple Access timing synchronization for UWB communications," IEEE Trans. Wireless Commun.,vol. 7, no. 11, pp. 4497-4501, Nov. 2008.
[32] Yang L. and Giannakis G. B., "Timing ultra-wideband signals with dirty templates," IEEE Trans. Commun., vol.53, Nov, 2005, pp. 1952-1963.
[33] Sun Q. and Lv T., "An Accurate Pulse-Level Timing Acquisition Scheme for UWB Signals," The Third Advanced International Conference on Telecommunications, 2007. AICT 2007. pp.10 - 10, May 2007.
[34] Brent Parr, ByungLok Cho, Kenneth Wallace, and Zhi Ding, "A Novel Ultra-Wideband Pulse Design Algorithm," IEEE. Commun. Lett., vol. 7, no. 5, pp.219-221. May 2003.
[35] Aiello, G. R., Rogerson, G. D, "Ultra-wideband wireless systems," IEEE Microw. Mag. Vol. 4, no. 2, pp. 36 - 47, Jun. 2003
[36] Clabaugh, D.J., Temple, M.A., Raines, R.A., Canadeo, C.M.," UWB multiple access performance using time hopped pulse position modulation with bior-thogonal signaling" 2003 IEEE Conference on Ultra Wideband Systems and Technologies, pp. 330 - 333, Nov. 2003
[37] Sadler B. M. and Swami A., "On the performance of UWB and DS-spread spectrum communication systems," In Proc. Conf.Ultra-Wideband systems and Technologies, pp. 289-292, May 2002.
[38] Foerster J. R., "The performance of a direct-sequence spread ultra-wideband system in the presence of multipath, narrowband interference, and multiuser interference," In Proc. Conf. Ultra-Wideband systems and Technologies, pp. 87-92, May 2002.
[39]Boubaker N.and Letaief K.B.,"Performance analysis of DS-UWB multiple access under imperfect power control," IEEE Trans.Commun.,vol.52,no.9,pp.1459-1463,Sep.2004.
[40]Saleh A.A.M.and Valenzuela R.A.,"A statistical model for indoor multipath propagation," IEEE J.Sel.Areas Commun.,vol.sac-5,no.2,pp.128-137,Feb.1987
[41]Foerster J.and Li Q.,"UWB channel modeling contribution from Intel," IEEE P802.15 Wireless Personal Area Networks Std.IEEE P802,Tech.Rep
[42]Irahhauten Z.,Nikookar H.and Janssen G.J.M.,"An overview of ultrawide band indoor channel measurements and modeling," IEEE Microw.Wireless Compon.Lett.,vol.14,no.8,pp.386-388,Aug.2004.
[43]IEEE P802.15 Working Group for WPANs,Channel Modeling Subcommittee Report Final,IEEE P802.15-02/368r5-SG3a,Nov.2002.
[44]Yang L.,"Ultra-wideband Communications:from concept to reality,"[Dissertation],The university of minnesota,2004
[45]葛利嘉,朱林,袁晓芳等(译).超宽带无线电基础:Understanding Ultra Wideband Radio fundamentals.北京:电子工业出版社,2005.
[46]Hu J.and Lv T.,"A Novel Chip-Level Algorithm for UWB Timing",IEEE Global Telecommunications Conference,pp.1-5,Dec.2008
[47]Carbonellil C.,Mengali U.and Mitra U.,"Synchronization and channel estimation for UWB signal," IEEE Global Telecommunications Conference,vol.2,pp.764-768.Dec.2003
[48]Scholtz R.A.,"Multiple access with time-hopping impulse modulation," in Proc.MILCOM,Oct.1993,pp.447-450.
[49]Lv Tiejun,Qiao Yongwei and Sun Qiang,"Training based synchronization and demodulation for UWB signals:algorithms and performance analysis," IEEE Trans.Commun.,(Accept aider revision).
[50]Tian Z.and Lottici V.,"Low-Complexity ML timing acquisition for UWB communications in dense multipath channels," IEEE Trans.Wireless Commun.,vol.4,no.6,pp.3031-3038,Nov.2005.
[51]周炯槃,庞沁华,续大我等.通信原理(上册).北京:北京邮电大学出版社,2002.
[52]Hoctor R.and Tomlinson H.,"Delay-hopped transmitted reference RF commu- nication," in Proc. Conf. Ultra wideband Systems and Technologies, May 2002,pp. 265-269
[53] Zhang H. and Goeckel D. L., "Generalized transmitted-reference UWB systems," IEEE Conference on Ultra Wideband Systems and Technologies,pp.147-151,Nov. 2003.
[54] Ho M., Somayazulu V., Foerster J. etc, "A differential detector for an ultra-wideband communications system," in Proc, Veh. Technol. Conf., Birmingham, AL May 2002, pp.265-269
[55] Yang L., Giannakis G B. and Swami A., "Noncoherent ultra-wideband (de)modulation," IEEE. Trans. Commun., vol. 55, no. 4, pp. 810-819, Apr. 2007.
[56] Antonio A. D'Amico and Lorenzo Taponecco, "A Differential Receiver for UWB Systems", IEEE Trans. Wireless Commun., vol. 5, no. 7, pp. 1601-1605,Jul. 2006.
[57] Lottici V., Andrea A. D. and Mengali U.,"Channel Estimation for Ultra-Wideband Communications," IEEE J. Sel. Areas Commun. vol. 20, no. 9, pp 1638-1645. Dec.2002
[58] Farahmand S., Luo X. and Giannakis G. B., "Demodulation with dirty templates for UWB impulse radios," IEEE Global Telecommunications Conference, 2005,vol. 4, pp. 2439-2443, Dec. 2005.
[59] Farahmand S., Luo X. and Giannakis G. B., "Demodulation and tracking with dirty templates for UWB impulse radio: algorithms and performance," IEEE Trans. Veh. Technol., vol. 54, no. 5, pp. 1595-1608, Sep. 2005.
[60] Rabbachin A. and Oppermann I., "Synchronization analysis for UWB systems with a low-complexity energy collection receiver," Proc. Joint UWBST &IWUWBS 2004, Kyoto, Japan, pp. 288-292, May 18-21, 2004.
[61] Oh M., Jung B. and Harjani R. etc, "A New Noncoherent UWB Impulse Radio Receiver," IEEE Commun. Lett., vol. 9, no.2, pp. 151-153, Feb. 2005.
[62] Stoica, L., Rabbachin, A., Oppermann, I., "Impulse Radio based Non-Coherent UWB Transceiver Architectures - An Example," IEEE Int. Conf. on UWB,pp.483 - 488 Sep. 2006
[63] Sun Q. and Lv T., "Data-aided efficient synchronization for UWB signals based on minimum average error probability," The Journal of China University of Posts and Telecommunications, vol. 15, no. 1, pp. 6-10, Mar. 2008.
[64] Homier E. A. and Scholtz R. A., "Rapid acquisition of ultra-wideband signals in the dense multipath channel," in Proc. IEEE Conf. UWB Syst. Technol., May 2002, pp. 245-250.
[65] Proakis J., Digital Communications, 4th Ed. New York: McGraw-Hill, 2001.
[66] Homier E. A., Synchronization of ultra-wideband signals in the dense multipath channel, [Ph.D. dissertation], Univ. Southern California, Los Angeles, CA,2004.
[67] Wang Z. and Yang X., "Blind channel estimation for ultra-band communi-caitions employing pulse position modulation," IEEE Signal Processing Letters,vol. 12, no.7, pp. 520-523, Jul. 2005.
[68] Cramer R. J., Scholtz R. A., and Win M. Z., "Evaluation of an ultrawideband propagation channel," IEEE Trans. Antennas Propag., vol. 50, no. 5, pp.561-570, May 2002.
[69] Yang L. and Giannakis G. B., "Blind UWB timing with a dirty template," in Proc. Int. Conf. Acoustics, Speech, and Signal Processing, Montreal, Quebec,Canada, May. 2004, pp. 509-512.
[70] Yang L. and Giannakis, G B. "Low-complexity training for rapid timing acquisition in ultra-wideband communications," in Proc. IEEE Globecom., vol. 2,Dec. 2003, pp. 769-773.
[71] Xu H. and Yang L., "Timing with dirty templates for low-resolution digital UWB receivers," The 2006 IEEE International Conference on Ultra-Wideband,pp. 321-326, Sep. 2006.
[72] Xu H. and Yang L., "Timing with dirty templates for low-resolution digital UWB receivers" IEEE Trans. Wireless Commun., vol. 7, no. 1, pp. 54-59, Jan.2008.
[73] Qiao Yongwei, Lv Tiejun and Ren Zhiyuan, "Direct-sequence codes based blind synchronization algorithm for UWB systems," The Journal of China Universities of Posts and Telecommunications, vol. 16, no. 3, pp. 45-51, Jun. 2009.
[74] Zhang R. and Dong X., "Synchronization and integration region optimization for UWB signals with non-coherent detection and autocorrelation detection,"IEEE Trans. Commun., vol. 56, no. 5, pp. 790- 798, May 2008.
[75] He N. and Tepedelenlioglu C., "Fast and low-complexity frame-level synchronization for transmitted reference receivers," IEEE Trans. Wireless Commun.,vol. 6, no. 3, pp. 1010-1023, Mar. 2007
[76] Yang L. and Giannakis G. B., "Optimal pilot waveform assisted modulation for ultrawideband communications," IEEE Trans.Wireless Commun.,vol.3,no.4,pp.1236-1249,Jul.2004.
[77]王玉孝.概率论与随机过程.北京:北京邮电大学出版社,2003.
[78]A.N.Shiryayev,Probability.New York:Springer-Verlag,1984.
[79]Hughes L.W.,"A simple upper bound on the error probability for orthogonal signals in white noise," IEEE Trans.Commun.,vol.40,no.4,p.670,Apr.1992.
[80]Hashemi H.,Impulse response modeling of indoor radio propagation channels.IEEE J.Sel.Areas Commun.,vol.11,no.7,pp.967-978,Sep.1993.
[81]Renzo M.D.,Annoni L.A.and Graziosi F.etc,"A novel class of algorithm for timing acquisition of differential transmitted reference UWB receiver:architecture,Performance analysis and system design," IEEE Trans.Wireless Commun.vol.7,no.6,pp.2368-2386,Jun.2008.
[82]Aedudodla S.R.,Vijayakumaran S.and Wong T.F.,"Acquisition of direct -sequence transmitted reference ultra-wideband signals," IEEE J.Sel.Areas Commun.vol.24,no.4,pp.759-765,Apr.2006.
[83]Ying Y.,Ghogho M.,and Swami,"Code-assisted synchronization for UWB-IR systems:algorithms and analysis," IEEE Trans.Signl Process.,vol.56,no.10,pp.5169-5180,Oct.2008.
[84]Ibrahim J.and Buehrer R.M.,"Two-stage acquisition for UWB in Dense Multipath,"IEEE J.Sel.Areas Commun.,vol.24,no.4,pp.801-807,Apr.2006.
[85]Huang Y.and Wang J.,"Two-stage acquisition in time-hopping impulse radio systems for UWB communications," IEEE Trans.Wireless Commun.vol.6,no.10,pp.3578-3588,Otc.2007.
[86]Tian Z.and Giannakis G.B.,"A GLRT approach to data-aided timing acquisition in UWB radios-Part I:algorithms," IEEE Trans.Wireless Commun.,vol.4,no.6,pp.2956 -2967,Nov.2005.
[87]Shin,D.H.,Cho Y.H.and Park D.J.,"A New Synchronization Scheme Exploiting Mean Energy Profile in UWB Non-Coherent Receiver," IEEE Int.Conf.Commun.,ICC'2006,vol.12,pp.5721-5725,Jun.2006.
[88]Wang J.,Mai L.and Peng Y.etl,"An energy-proportion synchronization method for IR-UWB Communications," Proc.IEEE Symposium on Circuit and Systems (ISCAS 2007),New Orleans,pp.2578-2581,May.2007.
[89]乔永伟,吕铁军.一种新的基于能量捕获的快速UWB同步算法.吉林大学学报(工学版).2009年第5期.
[90]张贤达.矩阵分析.北京:清华大学出版社,2004.
[91]Rabbachin,A and Oppermann,I," Comparison of UWB transmitted reference schemes," IEE Proc.Commun.,vol.153,no.1,pp.136-142,Feb.2006.
[92]Rabbachin,A.,Oppermann,I."Comparison of UWB auto-correlation and transmitted reference schemes," IEEE Int.Conf.UWB'2005,pp.497-501,Sep.2005.
[93]Qiao Yongwei and Lv Tiejun,"A blind synchronization and demodulation algorithm for UWB-IR communications," The 20th Personal,Indoor and Mobile Radio Communications Symposium 2009(PIMRC'09),(Submitted).
[94]Qiao Yongwei and Lv Tiejun,"Pseudo random time-hopping codes based joint blind synchronization and demodulation algorithm for UWB-IR systems," The 20th Personal,Indoor and Mobile Radio Communications Symposium 2009(PIMRC'09).Submitted
[95]Amico A.A.D',Mengali U.and Taponecco L.,"Synchronization for differential transmitted reference UWB receivers," IEEE Trans.Wireless Commun.,vol.6,no.11,pp.4154-4163,Nov.2007
[96]牛少彰.工程数学:复变函数.北京:北京邮电大学出版社,2004.
[97]Skelton Adam and Fu Shengli,"An improved conditional maximum-likelihood detector for noncoherent UWB communication," IEEE Commun.Lett.,vol.13,no.1,pp.7-9,Jan.2009.
[98]Qiao Yongwei and Lv Tiejun,"Blind synchronization and low-complexity demodulation for DS-UWB systems".IEEE GLOBECOM'2009.(Submitted)
[99]Qiao Yongwei and Lv Tiejun."A joint synchronization and demodulation scheme for UWB systems," IEICE Trans.Commun.,(Submitted).
[100]Chao Y.and Scholtz R.A,"Optimal and suboptimal receivers for ultra -wideband transmitted reference systems" IEEE GLOBECOM '03,vol.2,pp.759-763,vol.2,Dec.2003.
[101]Luo X.,and Giannakis G.B.,"Efficient synchronization-demodulation for UWB ad hoc access:performance analysis and comparisons with RAKE," IEEE 6th Workshop on Signal Processing Advances in Wireless Communications,pp.900-904,Jun.2005.
[102]Qiao Yongwei,Lv Tiejun and Zhang Lin,"A new blind synchronization algorithm for UWB-IR systems," The 2009 IEEE 69th Vehicular Technology Conference,VTC'2009-Spring,pp.1-5,Apr.2009.
[103]RCD Components Inc.[Online].http://www.rcd-comp.com/rcd/rcdpdf/a0805-sa0805-a1405-a1410.pdf.
[104]Casu M.R.and Durisi G.,"Implementation Aspects of a Transmitted Reference UWB Receiver," Wireless Communications and Mobile Computing,vol.5,no.5,pp.537-549,May 2005.
[105]L.Feng and W.Namgoong,"An Oversampled Channelized UWB Receiver with Transmitted Reference Modulation," IEEE Trans.Wireless Commun.,vol.5,no.6,pp.1497-1505,Jun.2006
[106]Goeckel D.L.and Zhang Q.,"Slightly frequency-shifted reference Ultra -Wideband(UWB) Radio," IEEE Trans.Communi.,vol.55,no.3,pp.508-519,Mar.2007
[107]Zhao Linli,Lv Tiejun and Qiao Yongwei,"A novel m-Sequence coded transmitted -reference UWB system," The Journal of China Universities of Posts and Telecommunications(Accept after revision).
[108]Urkowitz H."Energy detection of unknown deterministic signals," Proceeding of the IEEE,vol.55,no.4,pp.523-531,Apr.1967
[109]盛骤,谢式千,潘承毅.概率论与数理统计(第四版).北京:高等教育出版社,2008.
[110]Vantrees,H.L.,Detection,Estimation,and Modulation Theory:检测、估值与调制理论.北京:电子工业出版社,2003.
